Strain effects of nuclear explosions in Nevada

Abstract

abstract The University of Nevada's three-component quartz-rod strain meter installation at Round Mountain, Nevada (38°42.1′N, 117°04.6′W) has recorded a number of underground nuclear explosions at the Nevada Test Site, beginning with the megaton-sized JORUM event September 16 1969. Both that explosion and the larger HANDLEY event on March 26 1970 produced static strain offsets of a few parts in 109 at Round Mountain. These offsets did not decay within the first few hours after the explosions. In both cases, the strain offsets were in the sense of ground extension radial to the shot point, which is inconsistent with the assumption of a pure compressive source of strain. The strain-change ellipse for the HANDLEY event was found to have a major strain axis of 11 × 10−9 extensional, oriented N 34°W, and a minor axis of 7.4 × 10−9 compressional. A single-component strain meter at Mina, Nevada, (38°26.3′N, 118°9.3′W) was operated for the HANDLEY event, and recorded a strain offset of 2.6 × 10−9 in the direction N 74°E. Strain offsets at the time of the largest collapse events following HANDLEY were observed at Round Mountain. These offsets had the same sense on each component as those following the explosion itself. This is interpreted as support for the hypothesis that the strain changes are tectonic in origin, and the explosion initiates the strain release. Small offsets were observed for three smaller explosions out of a total of 13 studied. The relationship between body-wave magnitude mb and maximum dynamic strains at Round Mountain may be described empirically by the equation Log S = − 13.4 + 1.10 mb. Because of its high sensitivity and stability, the Round Mountain strain meter is capable of obtaining useful measurements of dynamic and static strain effects of intermediate- to large-sized explosions, at distances ranging from 160 to 200 km.